Method of rendering a substrate selectively non-wettable chip carrier with enhanced wire bondability

ABSTRACT

A substrate that is substantially non-wettable to adhesive resin is disclosed. The substrate is coated with a fluorinated silane composition. Preferable fluorosilane compositions include perfluoroalkyl alkylsilanes of Formula III:wherein R5 is a perfluoroalkyl alkyl radical; R6 is alkyl or alkenyl; X is acetoxy, halogen or alkoxy; n is 1 or 2; and m is 0 or 1. The composition is preferably applied in solution and upon evaporation of the solvent, forms a durable, non-wetting, yet well-adhering surface. In a preferred embodiment, the substrate is a chip carrier with enhanced wire bondability for use in the manufacture of a semiconductor device.

TECHNICAL FIELD

This invention relates generally to a substrate that is selectivelynon-wettable to adhesive resin and more particularly, the inventionrelates to a chip carrier with enhanced wire bondability that has beentreated with a fluorine-containing compound.

BACKGROUND ART

Plastic chip carriers are typically comprised of an organic substrate,such as a polyimide, having areas of metallic circuitry and wire bondpads. One of the initial stages of the assembly of a chip carrier istypically a board-attach process, during which an organic substrate isattached to a lead frame by means of a thixotropic organic adhesive,such as, for example, an epoxy-based adhesive, an acrylic-based adhesiveor a silicone. The adhesive is applied to the lead frame and thesubstrate is then placed onto the adhesive. The assembly may then beheated to assist in the cure of the adhesive, strengthening theattachment between the substrate and the lead frame. Similar adhesivesand processes are used in later stages of device assembly, such as in adie-attach process when integrated circuit chips or devices are bondedto the chip carrier. Depending on the design of the chip carrier, it maynot contain a lead frame. By necessity, a chip carrier will alwayscontain a die and most commonly a back-bonded die which isinterconnected via wire bonding.

Although the adhesives used during the various stages of device assemblyare fairly viscous, they have a propensity to bleed and spread out awayfrom the point of attachment. For example, during the board-attachprocess, resin from the adhesive often bleeds out from the periphery ofthe chip carrier attachment area, and spreads up the edges of the chipcarrier onto the circuitized upper surface, where it can contaminate thewire bond pads and render them non-bondable. This condition will causesignificant problems during later assembly steps when the bond sites areneeded to complete necessary electrical connections. As the resinspreads away from the attachment area, it can contaminate not only thewire bond sites, but also any portions of a soldermask which may lie inthe near vicinity.

The problems associated with adhesive resin bleed are even morepronounced when the chip carrier has been treated with a plasmacontaining oxygen and/or argon, prior to the application of theadhesive. Such plasma treatment is frequently employed to clean the wirebond sites and to roughen up the substrate surface prior to assembly ofthe semiconductor device.

Resin bleed is also encountered during other stages of semiconductordevice assembly. For example, during the die-attach process, anelectrically or non-electrically conductive adhesive is used, and ittoo, can bleed out along the periphery of the die attachment area andspread out over adjacent areas where electrical connections ultimatelyneed to be made.

Various methods for reducing resin bleed have been developed. Forexample, the chip carrier surface may have a recess at the point ofattachment of the die, such that the die and adhesive will be recessedbelow the adjoining areas o f the chip carrier where electrical bondingsites are located. As a drawback to this method, not all integratedcircuit assemblies provide the option of a recessed cavity in thecarrier surface. Very large scale integrated circuit (VLSI) assemblies,for example, require a large number of bonding sites and these are atthe same level as the die attachment surface.

U.S. Pat. No. 5,409,863, issued Apr. 25, 1995, teaches a method forcontrolling adhesive spread during a die-attach process. This methodincorporates a low profile barrier, such as a solder mask ring, into thechip carrier structure. The barrier surrounds the perimeter of the dieattachment area, preventing the spread of adhesive resin onto theadjacent bonding sites on the chip carrier.

In light of the many problems associated with adhesive resin bleed, asubstrate, such as a chip carrier, that is not subject to thisphenomenon, and thus has enhanced wire bondability, is thereforedesirable. Furthermore, because of this desirability, a method forrendering a substrate substantially n on-wettable to adhesive resin, andtherefore not subject to resin bleed, is especially desirable.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, a substrate,such as a chip carrier, with enhanced wire bondability is provided. Thesurfaces of the substrate, which may be both organic and metallic, arecoated with a fluorosilane composition. The coating renders thesubstrate substantially non-wettable, yet well-adhering, to adhesiveresin, thus preventing the resin from spreading away from the point ofattachment and contaminating other areas of the substrate.

According to one aspect of the present invention, a fluorosilane iscombined with an appropriate solvent and the resulting solution is thenapplied to the surfaces of a substrate by any conventional method andallowed to dry. The application of the fluorosilane composition has beenshown to render both organic and the metallic surfaces of a substratesubstantially non-wettable to adhesive resin and therefore, free fromresin bleed during an attachment process. When used in the context ofthe present invention, the term “non-wettable” is not to be confusedwith non-adherent as the disclosed process does not affect the qualityof the adhesion between either the die attach or the board attachadhesives and the treated surfaces.

In a preferred embodiment of the invention, the substrate is a chipcarrier. In this embodiment, the fluorosilane coating provides the chipcarrier with enhanced wire bondability due to the absence of resin bleedand the associated wire bond pad contamination.

DEFINITIONS

The following terms have the indicated meanings within the context ofthe present invention. “Alkyl” is intended to include linear, branchedor cyclic hydrocarbon structures and combination thereof. “Lower alkyl”refers to alkyl groups of from 1 to 8 carbons. Examples of lower alkylgroups include methyl, ethyl, propyl, isopropyl, butyl, s- and t-butyl,pentyl, hexyl, octyl, cyclopropylethyl, bornyl and the like. Preferredalkyl groups are those of C₃₀ or below.

“Perfluoroalkyl” refers to alkyl groups wherein each of the H atoms hasbeen substituted by a F atom. Preferred perfluoralkyl groups are of theformula C_(n)F_(2n+1), wherein n is an integer from 1 to 30.

“Cycloalkyl” is a subset of alkyl and includes cyclic hydrocarbon groupsof from 3 to 8 carbon atoms. Examples of lower cycloalkyl groups includec-propyl, c-butyl, c-pentyl, norbonyl and the like.

“Alkoxyl” refers to groups of from 1 to 8 carbon atoms of a straight,branched or cyclic configuration and combinations thereof attached tooxygen. Examples include methoxy, ethoxy, propoxy, isopropoxy,cyclopropyloxy, cyclohexyloxy and the like.

“Halogen” includes F, Cl, Br and I.

It is intended that the definitions of any substituent or symbol (e.g.,X) in a particular molecule be independent of its definition elsewherein the same molecule. Thus, —SiX₃ represents —SiCl₃, —Si(OCH₃)₃,—Si(CH₃)Cl₂, —Si(OCH₂CH₃)₂CH₃, etc.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with the principles of the present invention, a substrateis coated with a fluorosilane composition. Such treatment renders bothorganic and inorganic surfaces of the substrate substantiallynon-wettable to adhesive resin and provides the surfaces with reduced tonegligible resin bleed contamination. In a preferred embodiment, thesubstrate is a semiconductor chip carrier. In this embodiment, adhesivesused during device assembly steps are prevented from bleeding andspreading onto the wire bond sites, thus providing the chip carrier withenhanced wire bondability.

The principles of the present invention can be applied to any organicresinous material used to for m the underlying surface of a substrate ofa semiconductor chip carrier. Examples of such materials include, forexample, epoxy-based resins, epoxy re sin s reinforced with woven ornon-woven fiberglass, cyanate esters, cyanate/epoxy blends, polyimidesand bismoleimide triazene resins.

In addition to coating the organic components of the substrate, thefluorosilane composition also coats any inorganic materials present onthe substrate, such as those used to form the circuit lines, the groundpads and the wire bond sites. These inorganic materials include, forexample, copper, from which the circuitry is formed and gold, whichalong with nickel is plated over the copper circuitry to provide a wirebondable-surface and to provide protection against corrosion. Palladiumcan also be employed either directly over copper or in conjunction withgold and/or nickel. It has been determined that the application of thefluorosilane composition does not adversely effect the bondability ofthe metallic sites, nor the integrity of subsequent electricalconnections made using the coated bond sites.

The fluorosilane coating also coats any other organic materials presenton the surface of the substrate, such as in the case of a chip carrier,a soldermask. These materials are also rendered substantiallynon-wettable to adhesive resin. Examples of such materials includeepoxy-based and acrylate-based resins, as well as combinations thereof.An example of a frequently used epoxy/acrylate-based soldermask materialis, “Vacrel”, available from E. I duPont de Nemours Corporation,Wilmington, Del.

In one aspect of the invention, a fluorosilane is combined with asuitable solvent at a concentration of preferably, about 0.005 to 5percent by volume, and the resulting solution is then applied onto asubstrate and allowed to dry, preferably in air at room temperature. Thecoated substrate may be rinsed with, for example, water, prior todrying. To facilitate curing of the fluorosilane coating, the coatedsubstrate may be exposed to a heat source, for example, by baking at atemperature of about 100 to 150° C. for about 15 to 30 minutes, althoughhigher temperatures and shorter bake times may be used. For example,cure cycles of about 2 to 5 minutes at about 200 to 250° and moreparticularly, of about 3 minutes at about 250° are suitable.

Measurements obtained by the liquid drop method, utilizing a Goniometerand a liquid reactive resin, e.g., Union Carbide ERL-4299, demonstratethat the contact angle for a fluorosilane coated substrate surface issignificantly higher than that for a non-treated surface of the samesubstrate. Contact angles of less than about 25 degrees on either anorganic or a metallic surface, indicate that the surface has apropensity to be wettable and therefore to be susceptible to adhesiveresin bleed.

It has been demonstrated that the contact angles of non-treatedpolyimide and gold surfaces range from about 6 to 25 degrees. In sharpcontrast, the same surfaces, following treatment with a fluorosilanecomposition of the present invention, exhibit contact angles in therange of about 42 to 60 degrees.

The fluorosilanes suitable for use in this application are chosen fromthose having at least one hydrolyzable group and at least onenonhydrolyzable fluorine-containing organic group attached to a siliconatom. In accordance with the principles of the invention, thehydrolyzable group is involved in a reaction between the surfaces of thesubstrate and the fluorine-containing organic group donates the desirednon-wetting properties to the treated substrate.

Suitable fluorosilanes are those of Formula I:

R² _(m)SiR³ _(4-m)  I

wherein:

R² is a fluorine-containing organic group;

R³ is a hydrolyzable group; and

m is 1 or 2.

In general, the non-wetting properties donated to the substrate by thefluorosilane coating improve with an increase in the degree offluorination of the terminal region of R². Thus, R² will preferablycontain at least one CF₃— group in the terminal region.

R² may be any suitable organic group, and preferably is a saturatedorganic group such as, for example, alkyl, alkoxyalkyl oralkylcarboxyalkyl. Preferred R² groups have the structure:

X₃C—(Y)_(x)—(Z)_(y)—(CH₂)_(z)—

wherein:

X is F or CF₃;

Y is CF₂, CF(CF₃) or C(CF₃)₂;

Z is a divalent atom or group;

x is 0 or a positive integer;

z is 0 or a positive integer; and

y is 0 or 1.

Examples of R² groups include:

CF₃(CF₂)₉(CH₂)₂— CF₃ (CF₂)₅(CH₂)₂—

CF₃(CF₂)₃(CH₂)₂— CF₃ (CF₂)_(x)O(CH₂)₂—

(CF₃)₂CFO(CH₂)₃— (CF₃)₃CCF₂O(CH₂)₂—

One or more of the R² and R³ groups may be replaced by anothermonovalent atom or group, such as F, so long as the compound retains atleast one fluorine-containing organic group and at least onehydrolyzable group, and that the replacement atom or group does notinhibit hydrolysis or adversely affect the non-wetting properties of thefluorosilane coating to an undesirable extent.

In accordance with this modification, suitable fluorosilanes may also beof Formula II:

R² _(m)SiR³ _(n)R⁴ _(p)  II

wherein:

R² is a fluorine-containing organic group;

R³ is a hydrolyzable group;

R⁴ is a non-hydrolyzable atom or group other than R²;

m is 1 or 2;

n is 1, 2 or 3;

p is 0, 1 or 2; and

the sum of m+n+p is 4.

Due to the improved anti-wetting properties associated with an increasein the fluorination of the terminal region of R², perfluorosilanes, andmore particularly, perfluoroalkyl alkyl silanes are especially wellsuited for application in accordance with the principles of the presentinvention.

Preferred perfluoroalkyl alkylsilanes are compounds of Formula III:

R⁵ _(n)R⁶ _(m)SiX_(4-(n+m))  III

wherein :

R⁵ is a perfluoroalkyl alkyl radical;

R⁶ is alkyl or alkenyl;

X is acetoxy, halogen or alkoxy;

n is 1 or 2; and

m is 0 or 1.

Preferred compounds of Formula III are those wherein n is 1.

Preferred R⁵ perfluoroalkyl radicals range from CF₃ to C₃₀F₆₁, morepreferably from C₆F₁₃ to C₁₈F₃₇, and most preferably from C₈F₁₇ toC₁₂F₂₅.

Preferred R⁶ groups are selected from the group consisting of methyl,ethyl, propyl and vinyl, with methyl being the most preferred.

Preferred radicals for X include acetoxy, ethoxy, methoxy, chloro, bromoand iodo.

Preferred compounds of Formula II are the perfluoroalkyl ethylsilanes.As previously discussed, the fluorosilane compositions of the inventionreact with the substrate surface on a molecular basis and theperfluoroalkyl ethylsilanes exhibit a strong surface bonding, thusproducing a coated substrate surface that provides a high contact angle.Examples of such compounds include perfluoroalkyl ethyltrichlorosilane,perfluoroalkyl ethyltriacetoxysilane, perfluoroalkylethyltrimethoxysilane, perfluoroalkyl ethyldichloro(methyl)silane andperfluoroalkyl ethyldiethoxy(methyl)silane.

Other fluorosilanes suitable for the present application are of FormulaIV:

wherein:

Y is alkyl, alkoxyl or aryl having at least one fluorine;

X is a hydrolyzable group; and

R⁷ is X, Y or alkyl.

Preferred compounds of Formula IV are those wherein Y is an aliphatichydrocarbon in which all hydrogens on a plurality of adjacent carbonsare replaced by fluorine.

Examples of compounds of Formula IV are described in U.S. Pat. No.5,194,326 and include: (3,3,3-trifluoropropyl)trichlorosilane,(3,3,3-trifluoropropyl)dimethylchlorosilane,(3,3,3-trifluoropropyl)methyldichlorosilane,(3,3,3-trifluoropropyl)methyldimethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-methyldichlorosilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchlorosilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-trichlorosilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-methyldichlorosilane,(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-dimethylchlorosilane,(heptafluoroisopropoxy)propylmethyldichlorosilane,3-(heptafluoroisopropoxy)propyltrichlorosilane and3-(heptafluoroisopropoxy)propyltriethoxysilane.

Preferably, the fluorosilane composition is applied onto the circuitizedsubstrate in solution. Suitable solvents include, for example,isopropanol, ethanol, hexane, heptane, methylene chloride, acetone,naphtha, toluene and water. More preferred solvents include fluorinatedhydrocarbon solvents, such as trichlorotrifluoroethane, andperfluorinated organic compositions such as perfluorocarbons. Thesolution may be applied by any conventional application technique, suchas, for example, dipping, flowing, wiping or spraying.

Preferred concentrations for the fluorosilane composition are within therange of about 0.005 to 5 percent by volume, and more preferably, withinthe range of about 0.05 to about 2.5 percent by volume. It has, however,been shown that solvent-free compositions, i.e., 100 percent reactivesilanes, also provide good anti-wetting properties to a treatedsubstrate.

Desired anti-wetting properties may be obtained with a mixture ofdifferent fluorosilane compositions. Examples of such mixtures include(3,3,3-trifluoropropyl)trimethoxysilane with phenyltrimethoxysilane, amixture that is known to be thermally stable; and(heptadecafluoro-1,1,2,2-tetrahydrodecyl)-1-trimethoxysilane withphenyltrimethoxysilane.

The preferred embodiment of the present invention is hereinafterdescribed in more detail by means of the following examples that areprovided by way of illustration and not by way of limitation.

EXAMPLES

The contact angles recited in the following examples were measured usinga Rame-hart, Inc. (Mountain Lakes, N.J.) Goniometer, Model No. 100-00115. The surface to be measured was placed in a horizontal position,facing upward, in front of a light source. A drop of water or organicliquid was placed on top of the surface so that the contours of thesessile drop could be viewed and the contact angle measured through thegoniometer telescope with a graduated circular protractor.

Control 1

A mixture comprised of about 70 ml of isopropyl alcohol and 30milliliters (mL) of water is carefully mixed and kept at roomtemperature. The mixture was then applied onto a chip carrier via a dipcoating method and allowed to dry at room temperature. The coated chipcarrier was then exposed to moderate heat of about 120° for about 15 to30 minutes. The contact angles formed by a sessile drop of an organiccylcoaliphatic epoxide diluent (ERL-4299) on both the gold and polyimidesurfaces of the chip carrier were then measured. The results are shownin Table 1.

Example 1

The protocol established in Control 1 was employed to coat a chipcarrier with a mixture comprised of about 2 mL of1H,1H,2H,2H-perfluorooctyltriethoxy silane, 140 mL of isopropyl alcoholand 60 mL of water. The coated carrier was allowed to dry at roomtemperature and then exposed to moderate heat of about 120° to 150° forabout 15 to 30 minutes. The efficiency of the treatment was againmeasured by the contact angle formed by a sessile drop of diluentERL-4299 on both the gold and polyimide surfaces of the chip carrier.The results are shown in Table 1.

Example 2

The protocol established in Example 1 was repeated, coating a chipcarrier with a mixture comprised of about 3 mL of1H,1H,2H,2H-perfluorooctyltriethoxy silane, 140 mL of isopropyl alcoholand 60 mL of water. The resulting contact angles are shown in Table 1.

Control 2

The contact angles on both the gold and polyimide surfaces of anon-treated chip carrier were measured in accordance with the protocolof Control 1. The results are shown in Table 2.

Examples 3-12

A series of mixtures as shown in Table 2, containing either no silane (2treatments were with a solvent only) or varying amounts of1H,1H,2H,2H-perfluorooctyltriethoxy silane or1H,1H,2H,2H-perfluoroalkyltriethoxy silane, in various solvents wereprepared and left at room temperature. A chip carrier was immersed inone of each of the various mixtures for a period of about 25 to 30seconds and then allowed to dry at room temperature. The chip carrierswere then exposed to moderate heat of about 120° to 150° for about 15 to30 minutes. The efficiency of each of the various treatments wasmeasured in accordance with the same protocol as in Control 2. Theresulting contact angles are shown in Table 2.

Using the established protocol, it was also determined that the contactangles did not significantly change after the chip carriers were allowedto stand at room temperature for about two hours. Separate testsemploying a die attach adhesive demonstrated an absence of adhesiveresin spreading on both the polyimide and gold surfaces of the chipcarrier using the disclosed treatments.

This invention has been described in terms of specific embodiments, setforth in detail. It should be understood, however, that theseembodiments are presented by way of illustration only, and that theinvention is not necessarily limited thereto. Modifications andvariations within the spirit and scope of the claims that follow will bereadily apparent from this disclosure, as those skilled in the art willappreciate.

TABLE 1 CONTACT ANGLE CON- (deg) CENTRATION POLY- GOLD TREATMENT (% Vol)IMIDE SURFACE Control 0.0% in 21 15 (70/30 isopropyl alcohol/water)1H,1H,2H,2H- 1.0% in 54 56 perfluorooctyltriethoxy (70/30 isopropylsilane alcohol/water) 1H,1H,2H,2H- 1.5% in 52 55 perfluorooctyltriethoxy(70/30 isopropyl silane alcohol/water)

TABLE II CONTACT ANGLE (deg) CONC. POLY- GOLD TREATMENT (%) SOLVENTIMIDE PAD Control 0.0 15 17 (No treatment Propylene Glycol 16 14monomethyl ether Butyl Carbitol 17 19 1H,1H,2H,2H- 0.5 Propylene Glycol53 52 perfluoroalkyltriethoxy monomethyl ether silane 1H,1H,2H,2H- 2.0Propylene Glycol 55 54 perfluoroalkyltriethoxy monomethyl ether silane1H,1H,2H,2H- 0.5 Butyl Carbitol/ 52 49 perfluoroalkyltriethoxy IsopropylAlc 50/10 silane 1H,1H,2H,2H- 0.5 Propylene Glycol 42 44perfluoroalkyltriethoxy monomethyl ether silane 1H,1H,2H,2H- 3.0Propylene Glycol 44 35 perfluoroalkyltriethoxy monomethyl ether silane1H,1H,2H,2H- 2.0 Butyl Carbitol 59 50 perfluoroalkyltriethoxy silane1H,1H,2H,2H- 0.5 Butyl Carbitol 54 46 perfluoroalkyltriethoxy silane

We claim:
 1. A method for selectively rendering a substrate non-wettableto an adhesive organic resin, said substrate comprising both organic andmetallic surfaces, said method comprising coating the organic andmetallic surfaces of the substrate with a single layer of a fluorosilanecomposition, said fluorosilane composition being applied directly ontosaid surfaces, and obtaining a substrate comprising both organic andmetallic surfaces that are selectively non-wettable to an adhesiveorganic resin, wherein an electronic device can be wire bonded to saidnon-wettable metallic surfaces without being impaired by resin bleedfrom said adhesive organic resin, and wherein said metallic surfacescomprise conductive metals for making electrical connections, whereinsaid conductive metals are selected from the group consisting of copper,gold, nickel, palladium, and combinations thereof.
 2. The method ofclaim 1, further comprising the step of attaching a wire to at least oneof said metallic surfaces coated with said single layer of saidfluorosilane composition.
 3. The method of claim 1 wherein the substrateis a chip carrier for use in the manufacture of a semiconductor device.4. The method of claim 1 wherein the fluorosilane composition is insolution at a concentration of about 0.005 to 5 percent by volume. 5.The method of claim 4 wherein the fluorosilane solution is comprised ofa perfluoroalkyl alkyl silane in a suitable solvent.
 6. A method forrendering a substrate selectively non-wettable to an adhesive organicresin, said substrate comprising both organic and metallic surfaces,said method comprising the sequential steps of: (a) providing asubstrate comprising both organic and metallic surfaces, wherein saidmetallic surfaces comprise conductive metals for making electricalconnections wherein said conductive metals are selected from the groupconsisting of copper, gold, nickel, palladium, and combinations thereof;(b) providing a solution comprised of a fluorosilane in a suitablesolvent, the solution having a concentration of about 0.005 to 5 percentby volume; (c) applying the solution directly onto both the organic andmetallic surfaces of the substrate to form a single layer; (d) allowingthe substrate surfaces to dry; and (e) obtaining a fluorosilane-coatedsubstrate wherein both said organic and metallic surfaces of saidsubstrate are selectively non- wettable to an adhesive organic resin,and wherein an electronic device can be wire bonded to said coatedmetallic surfaces without being impaired by resin bleed from saidadhesive organic resin.
 7. The method of claim 6 further comprisingbaking the dried fluorosilane-coated substrate at a temperature of about100 to 250° C. for a period of about 2 to 30 minutes.
 8. The method ofclaim 7 wherein the baking is at a temperature of about 120 to 150° C.for a period of about 15 to 30 minutes.
 9. The method of claim 6 whereinthe substrate is a chip carrier for use in the manufacture of asemiconductor device.
 10. The method of claim 6 wherein the solution isapplied to the surfaces of the substrate by dipping, flowing orspraying.
 11. The method of claim 6 wherein the fluorosilane is ofFormula I R² _(m)SiR³ _(4-m)  I wherein: R² is a fluorine-containingorganic group; R³ is a hydrolyzable group; and m is 1 or
 2. 12. Themethod of claim 11 wherein R² has the structureX₃C—(Y)_(x)—(Z)_(y)—(CH₂)_(z)— wherein: X is F or CF₃; Y is CF₂, CF(CF₃)or C(CF₃)₂; Z is a divalent atom or group; x is 0 or a positive integer;z is 0 or a positive integer; and y is 0 or
 1. 13. The method of claim 6wherein the fluorosilane is of Formula II R² _(m)SiR³ _(n)R⁴ _(p)  IIwherein: R² is a fluorine-containing organic group; R³ is a hydrolyzablegroup; R⁴ is a non-hydrolyzable atom or group other than R²; m is 1 or2; n is 1, 2 or 3; p is 0, 1 or 2; and the sum of m+n+p is
 4. 14. Themethod of claim 6 wherein the fluorosilane is a perfluoroalkylalkylsilane of Formula III R⁵ _(n)R⁶ _(m)SiX_(4-(n+m))  III wherein R⁵is a perfluoroalkyl alkyl radical; R⁶ is alkyl or alkenyl; X is acetoxy,halogen or alkoxy; n is 1 or 2; and m is 0 or
 1. 15. The method of claim14 wherein: n is 1; R⁵ is CF₃ to C₃₀F₆₁; R⁶ is methyl, ethyl, propyl orvinyl; and X is acetoxy, ethoxy, methoxy, chloro, bromo or iodo.
 16. Themethod of claim 14 wherein the fluorosilane is a perfluoroalkylethylsilane.
 17. The method of claim 6 wherein the fluorosilane is ofFormula IV

wherein: Y is alkyl, alkoxyl or aryl having at least one fluorine; X isa hydrolyzable group; and R⁷ is X, Y or alkyl.
 18. The method of claim17 wherein Y is an aliphatic hydrocarbon in which all hydrogens on aplurality of adjacent carbons are replaced by fluorine.
 19. The methodof claim 6, further comprising: (f) attaching a wire to at least one ofsaid metallic surfaces coated with said single layer of saidfluorosilane composition.